Self-lubricating bearing elements

ABSTRACT

Bearing composition: A. POLYARYLENE SULFIDE B. INORGANIC LUBRICANTS.

United States Patent 11 1 Campbell et a1.

SELF-LUBRICATING BEARING ELEMENTS Inventors: Mahlon E. Campbell,Overland Park, Kans; William D. Walker, Independence, Mo.

Assignee: Phillips Petroleum Company, Bartlesville, Okla.

Filed: Feb. 15, 1974 Appl. No.: 443,083

References Cited UNITED STATES PATENTS 11/1966 Graham 252/12 May 6, 19753,354,129 11/1967 Edmonds et a1. 260/37 R 3,567,504 3/1971 Hopkins et al252/12 3,592,783 7/1971 Edmonds l 252/12 3,730,893 5/1973 Bilow e1 :11252/12 Primary Examiner-De1bert E. Gantz Assistant Examiner-1. Vaughn[57] ABSTRACT Bearing composition:

a. polyarylene sulfide b. inorganic lubricants.

10 Claims, No Drawings 1 SELF-LUBRICATING BEARING ELEMENTS Thisinvention relates to self-lubricating molded composite materials.

In recent years a wide variety of polymeric materials have been used inthe formation of bearings or bearing surfaces. Polymeric materials whichhave been used as bearings include poly( tetrafluoroethylene),polyamides, polyacetals, phenolformaldehyde resins and the like. Suchmaterials have been used for forming bearing surfaces for use inapplications where additional lubrication is generally to be avoided andin medium to light load bearing applications. While bearings formed fromthe various polymeric materials have proven useful for many purposes,such bearings and bearing surfaces have limited utility due to theirinability to carry heavy loads and their instability to heat.

It is therefore an object of this invention to provide a novelself-lubricating bearing composition.

It is another object to provide a method for the preparation of a moldedself-lubricating bearing composition.

Other aspects, objects, and advantages of this invention will be readilyapparent to those skilled in the art from the reading of the followingdisclosure.

In accordance with one embodiment of the present invention there isprovided a self-lubricating bearing composition which consistsessentially of an arylene sulfide polymer and at least one solidlubricating component.

In another embodiment of the present invention there is provided amethod for the preparation of a molded, self-lubricating polymericbearing composite of an arylene sulfide polymer and at least one solidlubricating component, which comprises admixing the arylene sulfidepolymeric material and at least one solid lubricating component andthereafter molding the resultant admixture under conditions of time,temperature and pressure necessary to effect formation of the bearingcomposite.

In a further embodiment of this invention, such solid bearing compositeis formed by admixing the polymeric material and the solid lubricatingcomponent, heating the resultant admixture at a first temperature for afirst interval, and molding the thus-heated admixture as describedabove.

ln a still further and presently preferred embodiment of this inventiona solid, molded, self-lubricating polymeric composite of an arylenesulfide polymer and at least one solid lubricating component is preparedby a method which comprises the steps of:

a. admixing said polymer and at least one solid lubricating component;

b. heating the resulting admixture at a first temperature for a firstinterval;

c. thereafter heating the admixture at a second, higher temperature fora second interval;

(1. cooling and grinding the thus-heated admixture;

e. compressing the ground admixture of step (d) in a mold at a firstpressure;

f. heating the thus-compressed composition at a third temperature for athird interval;

g. thereafter, molding the composition of step (f) at a second pressure;

h. cooling the thus-molded composite under said second pressure to afourth temperature; and

i. thereafter removing from the mold the finished self-lubricatingcomposite.

The arylene sulfide polymers which are useful in the formation of thesolid, self-lubricating bearing composite materials of this inventionare those formed by the reaction of at least one polyhalo-substitutedmonocyclic aromatic compound with an alkali metal sulfide. Such polymersare well known in the art and are disclosed in US. Pat. No. 3,354,129 ofEdmonds and Hill. Such polymers should have an inherent viscosity of atleast 0.01, preferably at least 0.10, as measured in lchloronaphthaleneat 206 C. at a polymer concentration of 0.4 grams per 100 ml of solvent.Such polymers should have a crystalline melt point above about 400 F.

The solid lubricating components useful in the present invention arethose selected from the group consist ing of molybdenum disulfide,molybdenum diselenide, graphite, antimony trioxide, tungsten disulfide,tungsten diselenide and mixtures thereof. The lubricating component canbe of any suitable lubricating grade or quality. Where molybdenumdisulfide is used, it should be free of flotation oil.

In a presently preferred embodiment, the solid lubricating component isformed of a mixture of molybde num disulfide and antimony trioxidehaving a weight ratio of molybdenum disulfide to antimony trioxide inthe range of 35:65 to :25. In a more preferred embodiment, thelubricating component is a 55:45 by weight mixture of molybdenumdisulfide and antimony trioxide, respectively.

The proportion of such lubricating component to the arylene sulfidepolymer can vary over a wide range. The composition can contain fromabout 10 to about 90 weight percent lubricating component, based on thetotal composition, preferably from about 50 to about weight percentlubricating component.

The composition of this invention can also contain fillers which do notsubstantially lessen the improvement in physical properties of thecompositions into which they are incorporated. Such fillers includepigments, reinforcing materials such as glass fibers, asbestos fibers,carbon fibers, boron fibers, glass fiber fabric, wire mesh and the like.Powdered metals such as bronze, silver, nickel, cobalt and lead can alsobe employed. When used, such materials can be present in amounts rangingfrom 0 to about 80, preferably 0 to about 50 weight percent of the totalcomposite. The proportions of polymer, lubricating components and othercomponents (if any), are such that the mixture provides a moldablecomposition.

In the preparation of the self-lubricating molded composites of thisinvention, weighed quantities of the desired ingredients are firstblended or mixed thoroughly. Blending can be done in any suitable mannerusing conventional blending apparatus. The polymer and lubricatingcomponent ingredients should be in particulate form. Preferably, theingredients should be finer than 60 mesh (US. Standard Sieve Series).

lfdesired, an inert diluent can be employed in mixing of theingredients. Such diluent should be easily remov able from the admixturein order not to interfere with later processing steps. Examples ofsuitable diluents are the halogenated hydrocarbons.

The thus-mixed admixture is then heated in the presence of air at afirst temperature for a first interval. Generally, the first temperaturewill be in the range of about 25 to about 125 F., preferably about 50 toabout 100 F., below the melt point of the polymer. The melt point ofarylene sulfide polymers can be readily determined by differentialthermal analysis (DTA) by heating a 10 mg. sample of the polymer in aDTA appa ratus at a rate of 10 C. per minute. The melt point is takenfrom the DTA thermogram in a conventional manner. The time during whichthe mixture is held at such temperature will be sufficient to effectpre-cure and reduce the melt flow, and generally will range from 0.5 to72 hours, usually from about I to 24 hours.

The thus-heated admixture is then heated at a second, higher temperaturefor a second interval. Generally, the second temperature will be in therange of to [00 F. above the melt point of the polymer. The times duringwhich the mixture is held at such second temperature is in the range offrom about to about 90 minutes, usually from 30 to 60 minutes.

Following the second heating step, the admixture is cooled and ground toa convenient particle size, preferably 60 mesh.

The thus-ground admixture is then compacted in a mold at ambienttemperature under a compaction pressure in the range of 500 to 5,000psig. Reinforcing materials or structures such as fabrics of glass fiberor wire mesh can be incorporated into the molding operation at thistime.

The compacted admixture is then heated at compaction pressure to a thirdtemperature for a third interval. The third temperature should be in therange of 0 to about 400 F. above the melt point of the polymericmaterial. The time during which the admixture is held at this thirdtemperature under compaction pressure will be sufficient to produce thedesired configuration without significant thermal degradation of thepolymeric material. This time is dependent, inter alia, upon moldconfiguration. the polymeric material, particle size and the like. Ingeneral, this time will be in the range of one minute to about one hour.

The heated, compacted admixture is then molded at said third temperatureat a pressure in the range of 3,000 to l0,000 psig.

The thus-molded composite is then allowed to cool at molding pressure toa temperature of about 300 F. or lower, after which the molded articleis removed from the mold. If necessary, the molded article can bemachined to complete the desired configuration.

Although the present invention is described in terms of compactionmolding, it is not intended that the present invention be limitedthereto. Other molding methods, such as injection molding, can be used.

The self-lubricating compositions of this invention are useful in avariety of applications. The composites can be used as journal bearings,journal bushings, ballbearing cages. compressor pistons, end fittings,thrust washers, face seals, guides, valve seats, wear rings, gears, camsand the like.

In the examples which follow, the arylene sulfide polymer which wasutilized in preparing the self lubricating composite materials of thisinvention was a commercial poly(phenylene sulfide) (PPS) having thefollowing properties: inherent viscosity, about 0.17; melt flow, aboutl3.4 (after heating about 6 hours at 500 F. sulfur content, about 29.0weight percent; dichlorobenzene content, about 0.2 ppm; and a particlesize of 99% smaller than 60 mesh.

The solid lubricating components used in preparing the compositematerials of this invention were molybdenum disulfide having a particlesize in the range of 0.5 to 40 microns, and antimony trioxide having aparticle size of about 200 mesh.

EXAMPLE 1 Composite Preparation Solid, self-lubricating compositematerials of this invention were prepared according to the followingprocedure:

a. Weighed portions of each component were thoroughly mixed in a highspeed blender using a low boil ing liquid halohydrocarbon as a blendingaid.

b. The well mixed slurry was poured into a flat stainless steel pan andthe volatile blending aid was allowed to evaporate.

c. The pan was placed in an air-circulating oven at 500 F. for 12-14hours. The temperature was increased to 700 F. and held there for onehour.

d. The admixture was reground to powder form.

e. A portion of the ground powder was placed in a die and compacted atambient temperature under a pressure at 2,000 to 3,000 psig.

f. The die was then heated to 750 F. using radiofrequency modulationheating. The above temperature and pressure were maintained for 30minutes after which the pressure was increased to 3,000 to 4,000 psig.After 5 minutes at the increased pressure, the heat was turned off andthe composite and die were allowed to cool under load to 300 F. Thecomposite was then removed from the die and bored or otherwise machined,as necessary, to complete the specific bearing configuration.

The composite materials are identified as follows; amounts of eachcomponent are given in terms of weight percent, based on the totalcomposite:

High Temperature Compressive Strength The high compressive strength ofone of the composite materials of this invention was shown in a seriesof load deflection tests. Composite material A was formed into flat testspecimens having an approximate diameter of 0.9 inch according to theprocedure of Example I. The test specimens were ground flat to anapproximate thickness of 0.04 inch. Deflection measurements were madeusing a hydraulic press for loading and a dial indicator to determinethe amount of deflection at temperatures between ambient and 600 F.Tests were terminated when the dial indicator would not stabilize afterthe load was applied, thus indicating that yield stress had beenexceeded. The results of these tests are given in Table I.

T bl I the bearing by dead weighing the hangwr iii which the sphericalbearing was mounted. l izitli tru t station wa Temperature. CompressiveStrength. driven directly by it l it P AF synchronous llltlltll'. OF PS15 Torque was sensed by a linear transducer in contact Rum tempcwwm 24)with the load hanger. ii ique was recorded on an extcr Fill) Zinnia nalrecorder. Bushing. ournal and shall tciiipeiuitiires were monitored byJill inlrtircil pyronieter tit-titre in conjunction with thermocoupleThe test data contained in Table ll iiitliiile Ptf lltil These data showunusually high compressive strength gg I l i net of load (psi) and speed(lpini. test Lillftllllll for the bearing. Moreover. substantialstrength is re- V I y r 0 (hours), wear factor. coclticient ot iIlLllOlln l .iiiti tamed at temperatures as high as 600 F.

maximum shaft temperature.

Wear factor. K. was calculated using the formula EXAMPLE ill I 5 JournalBearing Tests K mm? Journal bearings were formed from compositionswherein r is radial wear in inches. i is load in psi. l' is A-Daccording to the procedure of Example I. by com velocity in (pot. and Tis time in hours.

Table ll Min Shall Rim Material 1 Pt I lwslll p lim ii'i l A 6U 352M! i54 iii llll l (.lw 3 B ill! 352M: 115 t liil r 3 llll 5523i l1] i o il llli' l: :llll 4 D Z4U ."tfillill 114 Ti" i'iiij l 5 t" in: 352% 125 i lll 171+ ll b l" llli 2832i! l fi' *lll lll li 1S Al i 7 G lZU 3528i] .42lllls' ill ill it H (iii 282M! 425 i ll I? ti 55 1 Qt! 264M} 7.? i311 llgi Nol measured pacting the composite materials directly into the aseRuns 14 illustrate that bearings p epared ritrortliii of spherical seatswhich were positioned within the die to the process ot this inventionctln'liit relatiiel ion before addition ol'the powdered material. Theresulting wear rates. coefficient of friction illltifltf. heat buildupmoldings were then bored to fit a 0.625 in. diameter in the test shaftas compared to the tw ninitreially artilltest shaft having a surfacefinish of 6-10 pin. rms. able materials oi runs 54% For purposes ofcomparison. several commercially i. lLXAlrlPLl: l\' available bearingmaterials were also tested. These mam l are jd tifi d as f n 4UOseiilatory Sliding Friction and wear lusts Dumld 5813 a product OfRogers p Ruger5- Oseillatory sliding friction (and wear tests were penCUrmcomammg pillliltetrafluomethylene formed using a sliding frictionand wear tester iiliiclt L molybdenum dlslllfidc fiber glassemploys aflZllOndltlll test coiiligiiiirtion. A dead weight DUIOld 4300 IIPFOdUCl of Rogers W-i 2 and lever system applies the load to the uppertest spit? Conn. containing bronze. PTFE and fiber glass. imen. Testloads from lfitl to F.5t'lll pounds can be rip G. Garlock DU, a productof Garloek, inc. Cherry plied to this test specimen which is in contactwith :1 Hill. NJ, a steel-back-porous bronze material steel wear plate.Contact area can be varied from til filled with PTFE and lead and havinga thin surface to 1.0 sq in. Contact stresses can he varied from ifitllayer of PTFE and lead, psi to limit) psi. The wear plate is driven inti nearly H F l CT 3 product 1 Rogers Corp R sinusoidal reciprocatingmotion by a crank. pitiniiii :iiitl Conn containing a i id hi d slider.Speed of the reciprocating wear plate is tltlltlhl PTFB able from Z to60 strokes per minute. Stroke is adjust 1 Rulon A a product f Dixon CorpBristol 1 able from i inch to 4 inel'ics iii in inch incrementsv Fl'li."Containing PTFE fiber grass and imn Oxide tion force is measured li tilsll'illll page link in the iron 3 r i t Commercial materials F G and Hwere purchased as straint linkage tit tilt. test spti iiiitn iltilti titiiiti is [L- off-the-shelf bushings. Materials E and l were pur Cordedi lull Numb" i 'll ti chased as flat Stock rhlch Vere machlncd to fitthe Th6 l'olllth Oi lflebh lehsllh tilt. t liLll ill rtiillt bearingconfiguration of this test. Bearings of materials E, G and l were 0.625in. diameter by 0.504 to 0.545 TAB] ii iii in. long and materials F andH were 0.5 in. diameter by 6.5 in. long Invention bearings A-D were 0.5in. diamen Material P P l l-t ii W p n 7 it) A 1500 iizniiii lli tiii :i

The ournal bearing tests were carried out on a high it A m n 35min 1 11speed journal bearing tester. Test shafts were hardened 6g I i l *2 r tl is, i .1 :3;

dowel pins having diameters appropriate to the beari4 3 my rrn i 1tlllri Ill ings under test. The journal was the ball of a standard 15 Eiii-4% i Q in. diameter spherical bearing. Load was applied to RunslO-i4 illustrate the low wear rate and coefficient of friction ofsliding bearings prepared according to this invention over a wide rangeof PV values as compared to the commercially available materialslybdenum disulfide and antimony trioxide in a weight ratio of molybdenumdisulfide to antimony trioxide ranging from 35:65 to 75:25.

2. The composition of claim 1 wherein said solid lutested in runs 15 andi6. bricating component is present in said composition in an approximateamount ranging from [0 to 90 weight EXAMPLE V percent. Ball BearingRetainer Tests The compos1t1on of claim 2 wherein said weight ratio is55:45. Ball bearing retainers (cages) e fabricated to 4. The compositionof claim 1 wherein said polymer cording to the method of the presentinvention for use i polyphenylene lfid In 8126 ge coma" Yp ballbearings: 5. A method of forming a solid self-lubricating com- 'ybeal'mg matenal 52100 SIeeLThe relamel's posite consisting essentiallyof an arylene sulfide polywere molded and/or mach ned t0 the d slr d(3-11 mer and at least one solid lubricating component seand Wldth.followed y drlllmg of the p 15 lected from the group consisting ofmolybdenum disul- The bearing assemblles were tested on a Rolling Elefidbd di l id graphite, antimony m ment Bearing Tester at various speeds,radial loads and id tungsten di lfid tungsten di l id d i temperaturesThe bearmgs were run completely y tures thereof which comprises thesteps of: with added lubl'lcama. admixing said polymer and at least oneof said solid The results of these tests are given in Table IV.inlubricating components; eluded in these tests were bearings havingSteel, P b. heating the resulting admixture at a first temperanolic andunfilled p0ly( phenylene Sulfide) retainers ture for a first interval;which were operated without added lubricant for comc. thereafter heatingsaid admixture at a second, parative purposes. higher temperature for asecond interval;

Table IV Test Retainer Speed Load (lb) Duration Bearing Run Material(rpm) Thrust Radial (hours) Condition Remarks 1? Steel 3450 i0 5 0.]Damaged Terminated due to high friction l8 Steel 3450 40 20 0.1 DamagedTerminated due to high friction l9 Phenolic 3450 i0 5 10.0 DamagedTerminated due to high friction 20 PPS 3450 i0 5 5.0 Damaged Terminateddue to high friction 2l A 3450 40 20 340 No damage Cage fracture 22 C3450 l0 5 300 No damage Ball pockets worn through 23 C 3450 40 20 600 Nodamage Ball pockets worn through 24 C 3450 40 20 600 No damage Nofailure 25 C 6400 10 5 22 No damage Cage fracture 26 C 10200 20 59 Nodamage Cage fracture 27 C l0200 40 20 l 13 No damage Retainer wornout-of-round 28" C 3450 40 20 256 No damage No failure "Heat added tooperate at 300" F.; all other tests at ambient temperature.

'Unl'illed p0ly(phcnylene sulfide). molding grade C-l00, availablecommercially from Phillips Petroleum Company.

The data in Table IV illustrate the ability of ball bearing retainersprepared according to the present invention to withstand high speeds andloading without additional lubrication. The steel retainers of runs 17and 18 were operable for only a matter of minutes. The syntheticretainers of runs l9 and 20 were operable for up to 10 hours. Incontrast. run 22 demonstrates that a bearing retainer of this inventionran for 300 hours under conditions similar to conditions used in controlruns 17, 19 and 20.

We claim:

1. A self-lubricating polymeric composition consisting essentially of anarylene sulfide polymer and a solid lubricating component consisting ofa mixture of mod. thereafter cooling and grinding said thus-heatedadmixture;

e. compressing the thus-ground admixture of step (d) in a mold at afirst pressure;

f. heating the thus-compressed composition at a third temperature for athird interval;

g. thereafter, molding the composition of step (f) at a second pressure;

h. cooling the thus-molded composition under said second pressure to afourth temperature; and

i. thereafter removing from the mold the finished self-lubricatingcomposite. 6. The method of claim 5 wherein said first temperature is inthe range of 25 to l25 F. below the melt point of said polymer and saidfirst interval is in the range of 0.5 to 72 hours;

said second temperature is in the range of 0 to 100 F. above the meltpoint of said polymer and said second interval is in the range of about10 to about minutes;

said first pressure is in the range of 500 to 5,000 psig',

said third temperature is in the range of 0200 F. above the melt pointof said polymer and said third interval is in the range of 1 minute toabout i hour;

said second pressure is in the range of 3,000 to 10,000 psig; and

said fourth temperature is not greater than 300 F.

7. The method of claim 6 wherein said solid lubricating component ispresent in said composite in an approximate amount ranging from 10 to 90weight percentv 8. The method of claim 7 wherein said solid lubricatingcomponent is a mixture of molybdenum disulfide and antimony trioxide ina weight ratio of molybdenum

1. A SELF-LUBRICATING POLYMERIC COMPOSITION CONSISTING ESSENTIALLY OF ANARYLENE SULFIDE POLYMER AND A SOLID LUBRICATING COMPONENT CONSISTING OFA MIXTURE OF MOLYBDENUM DISULFIDE AND ANTIMONY TRIOXIDE IN A WEIGHTRATIO OF MOLYBDENUM DISULFIDE TO ANTIMONY TRIOXIDE RANGING FROM 35:65 TO75:25
 2. The composition of claim 1 wherein said solid lubricatingcomponent is present in said composition in an approximate amountranging from 10 to 90 weight percent.
 3. The composition of claim 2wherein said weight ratio is 55:
 45. 4. The composition of claim 1wherein said polymer is polyphenylene sulfide.
 5. A METHOD OF FORMING ASOLID SELF-LUBRICATING COMPOSITE CONSISTING ESSENTIALLY OF AN ARYLENESULFIDE POLYMER AND AT LEAST ONE SOLID LUBRICATING COMPONENT SELECTEDFROM THE GROUP CONSISTING OF MOLYBDENUM DISULFIDE, MOLYBDENUMDISELENIDE, GRAPHITE, ANTIMONY TRIOXIDE, TUNGSTEN DISULFIDE, TUNGSTENDISELENIDE, AND MIXTURES THEREOF WHICH COMPRISES THE STEPS OF: A.ADMIXING SAID POLYMER AND AT LEAST ONE OF SAID SOLID LUBRICATINGCOMPONENTS;55 B. HEATING THE RESULTING ADMIXTURE AT A FIRST TEMPERATUREFOR A FIRST INTERVAL; C. THEREAFTER HEATING SAID ADMIXTURE AT A SECOND,HIGHER TEMPERATURE FOR A SECOND INTERVAL; D. THEREAFTER COOLING ANDGRINDING SAID THUS-HEATED ADMIXTURE; E. COMPRESSING THE THUS-GROUNDADMIXTURE OF STEP (D) IN A MOLD AT A FIRST PRESSURE; F. HEATING THETHUS-COMPRESSED COMPOSITION AT A THIRD TEMPERATURE FOR A THIRD INTERVAL;G. THEREAFTER, MOLDING THE COMPOSITION OF STEP (F) AT A SECOND PRESSURE;H. COOLING THE THUS-MOLDED COMPOSITION UNDER SAID SECOND PRESSURE TO AFOURTH TEMPERATURE; AND I. THEREAFTER REMOVING FROM THE MOLD THEFINISHED SELFLUBRICATING COMPOSITE.
 6. The method of claim 5 whereinsaid first temperature is in the range of 25* to 125* F. below the meltpoint of said polymer and said first interval is in the range of 0.5 to72 hours; said second temperature is in the range of 0* to 100* F. abovethe melt point of said polymer and said second interval is in the rangeof about 10 to about 90 minutes; said first pressure is in the range of500 to 5,000 psig; said third temperature is in the range of 0*-200* F.above the melt point of said polymer and said third interval is in therange of 1 minute to about 1 hour; said second pressure is in the rangeof 3,000 to 10,000 psig; and said fourth temperature is not greater than300* F.
 7. The method of claim 6 wherein said solid lubricatingcomponent is present in said composite in an approximate amount rangingfrom 10 to 90 weight percent.
 8. The method of claim 7 wherein saidsolid lubricating component is a mixture of molybdenum disulfide andantimony trioxide in a weight ratio of molybdenum disulfide to antimonytrioxide ranging from 35:65 to 75:25.
 9. The method of claim 8 whereinsaid weight ratio is 55:45.
 10. The method of claim 5 wherein saidpolymer is polyphenylene sulfide.